Dissociative personality disorder (multiple personality) is a severe mental disorder in which a person has more than one distinct identity or personality state. It is a condition in which a single person displays multiple distinct identities or personalities each with its own pattern of perceiving and interacting with the environment. Individuals with Dissociative personality disorder may also have post-traumatic symptoms such as nightmares, flashbacks, and startle responses or Post-Traumatic Stress.

Factors which can cause Dissociative personality disorder (multiple personality) are following:

• Dissociative personality disorder results from extreme and repeated trauma that occurs during important periods of development in childhood. The trauma often involves severe emotional, physical or sexual abuse. The person disconnects himself from the trauma and is therefore able to escape from the unbearable physical and emotional pain. The thoughts, feelings and memories of the event are dissociated from the mind of the person, as if they had never occurred.
• Dissociative personality disorder may run in families. There might be an inherited tendency to dissociate.
• Multiple personality disorder is sometimes triggered by organic causes. For instance, brain injury, temporal lobe epilepsy sometimes can lead to personality split. Other organic causes of multiple personality disorder include sleep loss, sensory deprivation and stroke.
• An important early loss, such as the loss of a parent also might be a cause of Dissociative personality disorder.